Zhang Peng, Li Hao, Wang Shuying, Chu Biwu, Chen Tianzeng, Ma Qingxin, Wang Yonghong, Yu Yunbo, He Hong
State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
Environ Sci Technol. 2024 Sep 10. doi: 10.1021/acs.est.4c03406.
Soot, primarily composed of elemental carbon (EC) and organic carbon (OC), is ubiquitous in PM. In the atmosphere, the heterogeneous interaction between NO and soot is not only an important pathway driving soot aging but also of central importance to nitrous acid (HONO) formation. It is commonly believed that the surface redox reaction between reductive OC and NO dominates the night aging of soot and the conversion of NO to HONO. However, completely differing from the currently popular explanation, we find here that the redox reaction between EC and NO can also drive the conversion of NO to HONO during soot aging. By combining in situ experiments with density functional theory (DFT) calculations, we proposed that the surface carbon vacancy defects on graphite/graphene-like EC should be a type of potential primary adsorption and reactive sites inducing the heterogeneous reduction of NO. We suggested a new mechanism that NO is reduced to form HONO on surface vacancy defects through the splitting of HO molecules, and the carbon atoms adjacent to surface vacancy are simultaneously oxidized to form hydroxyl-functionalized EC. This novel finding provides insights into the chemical mechanism driving the NO-to-HONO conversion and rapid soot aging, which expands our knowledge of the heterogeneous chemistry of soot in the atmosphere.
煤烟主要由元素碳（EC）和有机碳（OC）组成，在颗粒物中普遍存在。在大气中，NO与煤烟之间的非均相相互作用不仅是推动煤烟老化的重要途径，而且对亚硝酸（HONO）的形成至关重要。人们普遍认为，还原性OC与NO之间的表面氧化还原反应主导了煤烟的夜间老化以及NO向HONO的转化。然而，与目前流行的解释完全不同，我们在此发现，EC与NO之间的氧化还原反应在煤烟老化过程中也能推动NO向HONO的转化。通过将原位实验与密度泛函理论（DFT）计算相结合，我们提出，石墨/类石墨烯EC上的表面碳空位缺陷应该是一类潜在的主要吸附和反应位点，可诱导NO的非均相还原。我们提出了一种新机制，即NO通过HO分子的分裂在表面空位缺陷上被还原形成HONO，并且与表面空位相邻的碳原子同时被氧化形成羟基官能化的EC。这一新颖发现为驱动NO向HONO转化和煤烟快速老化的化学机制提供了见解，扩展了我们对大气中煤烟非均相化学的认识。
